std.testing: add writeZigFile for TmpDir

* remove need for manual string concatenation for building binaries in test blocks
* include small program snippet to show how to get binary path with subslicing

1 files changed, 37 insertions, 0 deletions

diff --git a/lib/std/testing.zig b/lib/std/testing.zig
index 004e2d0fa7..df2d6c7a43 100644
--- a/lib/std/testing.zig
+++ b/lib/std/testing.zig
@@ -374,6 +374,43 @@ pub const TmpDir = struct {
         self.parent_dir.close();
         self.* = undefined;
     }
+
+    /// Writes program string as zig file into tmp directory
+    /// Caller owns memory
+    ///
+    /// ```
+    /// const progstr = "pub fn main() void {}\n";
+    /// var it = try std.process.argsWithAllocator(std.testing.allocator);
+    /// defer it.deinit(); // no-op unless WASI or Windows
+    /// const testargs = try std.testing.getTestArgs(&it);
+    /// var tmp = std.testing.tmpDir(.{ .no_follow = true }); // ie zig-cache/tmp/8DLgoSEqz593PAEE
+    /// defer tmp.cleanup();
+    /// const zigfile_path = try tmp.writeZigFile(std.testing.allocator, progstr, "bruh");
+    /// defer std.testing.allocator.free(zigfile_path);
+    /// const binary = zigfile_path[0 .. zigfile_path.len - 4]; // '.zig' is 4 characters
+    /// try std.testing.buildExe(testargs.zigexec, zigfile_path, binary);
+    /// ```
+    pub fn writeZigFile(
+        self: *TmpDir,
+        alloc: std.mem.Allocator,
+        progstr: []const u8,
+        filename: []const u8,
+    ) ![]const u8 {
+        const tmpdir_path = try self.getFullPath(alloc);
+        defer alloc.free(tmpdir_path);
+        const suffix_zig = ".zig";
+        const zigfile_path = try std.mem.concat(alloc, u8, &[_][]const u8{
+            tmpdir_path,
+            std.fs.path.sep_str,
+            filename,
+            suffix_zig,
+        });
+        errdefer alloc.free(zigfile_path);
+        const zigfile = try std.mem.concat(alloc, u8, &[_][]const u8{ filename, suffix_zig });
+        defer alloc.free(zigfile);
+        try self.dir.writeFile(zigfile, progstr);
+        return zigfile_path;
+    }
 };
 
 fn getCwdOrWasiPreopen() std.fs.Dir {